The use of fundus imagers and ophthalmoscopes is well established as a means to non-invasively examine the retina of the human eye to aid in the detection and nature of ocular diseases. Such instruments inject light through the pupil of the eye and collect light reflected from the retina and passing back through the pupil.
This type of observation is well suited for the examination of the upper layers of the retina and routinely shows a bright optical nerve head (ONH) and blood vessels leading back to the ONH.
The layer below the retina, the choroid, remains substantially hidden from such observations because most of the incident light is reflected or absorbed before it reaches the choroidal layer. The choroid, also known as the choroidea or choroid coat, is a vascular layer containing connective tissue of the eye lying between the retina and the sclera, as shown in FIG. 1. In humans the thickness of the choroid is about 0.5 mm. The choroid provides oxygen and nourishment to the outer layers of the retina.
Non-invasive observation of the choroid can provide useful and significant information pertaining to a number of ocular diseases, such as choroidal melanoma and choroidal neovascularisation.